1 files changed, 32 insertions, 0 deletions
diff --git a/app/models/milestone.rb b/app/models/milestone.rb
index 84acba30b6b..2ff16e2825c 100644
--- a/app/models/milestone.rb
+++ b/app/models/milestone.rb
@@ -105,4 +105,36 @@ class Milestone < ActiveRecord::Base
   def author_id
     nil
   end
+
+  # Sorts the issues for the given IDs.
+  #
+  # This method runs a single SQL query using a CASE statement to update the
+  # position of all issues in the current milestone (scoped to the list of IDs).
+  #
+  # Given the ids [10, 20, 30] this method produces a SQL query something like
+  # the following:
+  #
+  #     UPDATE issues
+  #     SET position = CASE
+  #       WHEN id = 10 THEN 1
+  #       WHEN id = 20 THEN 2
+  #       WHEN id = 30 THEN 3
+  #       ELSE position
+  #     END
+  #     WHERE id IN (10, 20, 30);
+  #
+  # This method expects that the IDs given in `ids` are already Fixnums.
+  def sort_issues(ids)
+    pairs = []
+
+    ids.each_with_index do |id, index|
+      pairs << id
+      pairs << index + 1
+    end
+
+    conditions = 'WHEN id = ? THEN ? ' * ids.length
+
+    issues.where(id: ids).
+      update_all(["position = CASE #{conditions} ELSE position END", *pairs])
+  end
 end